Telephone system



Dec. 3, 1929.

E. E. HINRICHSEN 1,738,245

TELEPHONE SYSTEM Filed Nov. 1. 1928 5 Sheets-Sheet 1 Wnw Dec. 3, 1929. E. E. HINRICHSEN TELEPHONE SYSTEM Filed Nov. 1, 1928 5 Sheets-Sheet 3 13% NNW ATTORNEY Dec. 3, 1929. E. E. HINRICHSEN TELEFHONE SYS TEM Filed Nov. 1, 1928 5 Sheets-Sheet 4 QQQ //v VENTUR E. 'E. H/A/R/awsE/v By W MI M W M II w 1 QQ W mm \Sw A h t ATTORNEY ill Patented Dec. 3, 1929 Ei'l'AEh ATEN thhlfit.

EDWABD E. HINRIGll-ISEN, OF NEW YORK, N. Y., ASSIGNOR- TO BELL TELEPHGNE LABQRATORIES, INCDRFORATED, 0F NE'W YORK, N. Y., A CORPORATION G11? YORK TELEPHONE SYSTEM Application filed. November his invention relates to telephone systems and particularly to improvements in automatic switching systems.

An object is to simplify the equipment used in small capacity automatic. switching s" tenis such as pri ate branch exchange toms and to economically employ switches by utilizing them in the establishing of dilterent types of connections without detracting from their normal capacity and utility.

Another object of the invention is train the pe "ion snd the cor some simplified nature, while increafl capacity of the system.

l-leretotore, in the establishing i types of connections in systems o this pe, a. calling subscribers line is first extended through a. line tinder and alinl: circuit to connector. lit then a certain impulse code is received this original connection is released and a trunk line finder engaged to extend the connection to an idle trunk while it a usual series of iniipulses received the original connection is further ez-ztended through the conto Niall-'1- of dialer J J. r L

" nector.

According to one feature of the present invention the switches are more economically employed in that the original extension or the culling subscribefis line through a line finder and a linlt circuit to u connector, is re tained regardless of the type of connection desired from this point. It a special impulse code is received, the connector is actuated as a marker switch to-cause the trunk line tinder or hunting switch of an idle trunk to connect said trunk to the link circuit, whereupon the cmuicctor is relented; while it a usual series of impulses is received the connector is actuated to extend the connection therethrough in t is usual manner. The arrongmient is such that the normal cupecity oi the connector. for

ding the usual connections therethrough is not decreased by the use of the connector as o marker switch.

Another feature of the invention is an urrangenient whereby the trunks may be divided in groups leading to dillerent points and the connectors actuated to marl; the particular groin in which the huntirn switch of an idle trunk shall be actuated.

1, 1923. Serial NO. 315,432.

Another feature of the invention is an ar rungement whereby connections maybe made from a trunk to it called subscribers line. In this case the hunting switch ot the seized trunk is actuated to hunt for an idle link circuit, whereupon the associated connector may be actuated by incoming impulses to select the desired subscribefis line, while the line finder associated with the seized link circuit is made busy.

Another festure of this invention is the provision of means for increasing the capacity of an exchange. Additional groups of subscribers lines may be equipped in the same manner as the iirst group except that the teruiinels oi the additional connectors are multipled to the first group of subscribers lines. Extragroups of hunting switches are also added having access to all the links in the system. The brushes of each group cl? such hunting switches are connected through lin {S to auxiliary connectors, the terminals of which are in turn multipled to the subscribers lines of a particular group.

lily this urrangmcnt, a sul'isi-icribcr in the first group may be connected to a subscriber in any one of the other groups by the dialing of a certain code. This certain code causes an idle one of the extra hunting switches, in the group having access to the particular group of subscribers {inning which the wanted subscribefis line may be "found, to be actuated to find the link with which the calling subscribers line is associated. The calling subscriber may then proceed to dial the wunted subscribers number and thereby cause the auxiliary connector associated with the seized hunting switch and link to be actuated to find the wanted subscribci"s line. Similarly, if a subscriber in a second or a third group desires to establish a connection with a subscriber in another of the additional groups the pro cedure is the same. It a subscriber in an additional group desires to call a subscriber in the first group, a rcgulor connector, associated with a link and line tinder throu h which the calling subscriber has been 0 tendech is not .ated to select the wanted subscribers line.

This invention has been illustrated in the accompanying drawings, in which Fig. 1 shows in diagrammatic form the arrangement for extending connections from several groups of subscribers lines at a private branch exchange;

Figs. 2, 3, 4, 5 and 6 illustrate the detailed circuits for one group of subscribers lines from which connections may be made;

Fig. 7 shows how Figs. 2 to 7 may be arranged for reading in connection with the specification.

Referring now to Fig. 1, this figure illustrates a typical grouping of subscribers lines in a private branch exchange, arranged in accordance with this invention. Three groups of subscribers lines have been shown; groups 1, 2 and 3, each of which may comprise 200-lines. These lines terminate in jacks at the private branch exchange operators position; group 1 in jacks 4; group 2 in jacks 5 and-group 3 in jacks 6. These groups of lines also terminate in line finders at 7, 8 and 9, respectively. The line finders are connected to groups of link circuits at 10, 11 and 12, connected respectively to groups of connector switches at 13, 14 and 15. These connector switches have access to the subscribers lines in group 1, hence a connection from a subscriber in groups 1, 2 or 3 to a subscriber in. group 1 will extend over a line finder in groups 7 ,8 or 9, a link in'the groups 10, 11 or 12 and aconnector in groups 13, 14 or 15. These three groups of connectors 13, 14 and 15 are further arranged .asmarking switches for causing hunting switches such as groups 16 to 22 to'be actuated to extend connections from the subscribers in these three groups to various points as will be explained hereafter.

For example, if a connection is desired from a subscriber in group '1 to a subscriber in group 2 the connection is extended over a line'finder in group 7, a link in group and a connector in group 13. The connector now acts as a marking switch to cause an idle trunk hunting switch 16 or 17 to be actuated to find the link in group 10, to which the calling subscriber of group 1 is connected. Hunting switches 16 to 19 are associated with auxiliary groups of connectors 23 to 26. A connection will therefore in this case be further extended through an auxiliary connector 23 or 24 to the desired subscribers line in group 2. If a connection is desired froma subscriber in group 1 tea subscriber in group 3 the pro- :cedure is the same except that a hunting switch 18 or 19 is actuated to find the link in group 10, t0 which the calling subscriber is connected and further extended through an auxiliary connector 25 or 26 to the wanted subscriber in group 3.

p In establishing a connection from a subscriber in any one of the groups 1, 2 or 3 to a subscriber in group 1 a three-digit number isused byrthe calling subscriber. The

first number is in this particular arrange ment either the numeral 2 or 3. The numeral 2 will select the first group of one hundred lines and the numeral 3 the second group of one hundred lines. This first digit therefore determinesin which group oi one hundred lines the called subscribers line is located. The second and third numerals may be any one of the numbers from 1 to O, the selection of the calling line being in this case made by a connector in either of the groups 13, 14 or 15, the connector serving in such a connection only as a connecting switch. If a connection is desired from a subscriber in groups 1, 2 or 3 to a subscriber in group 2 or 3, a tour-digit number IS used by the calling subscriber. The first digit causes the corresponding connector in group 13, 14 or to act as a marker and extend the connection to an auxiliary connector, the second digit causes the operation of the auxiliary connector to select the group of one hundred lines in which the desired subscriber is located, and the third and fourth digits select the wanted subscribers line.

Access may also be had from a subscriber in groups 1, 2 or 3 to the private branch exchange operators position. If such a connection is desired a connector in groups 13, 14 and 15 will act as a marker to cause a hunting switch in group to connect with the calling subscriber through the associated link circuit and establish a connection to the private branch exchange operator over a trunk in group 28, terminating in a jack at the private branch exchange operators position 29.

A connection may also be had, from groups 1, 2 or 3, over hunting switches in group 21, to a tie-line in group 30, said group of tielines leading to other private branch exchanges. In this case the connector in groups 13, 14 or 15 will act as a marker to cause an idle switch oi. group 21 and the associated trunk in group 30 to be selected.

The circuits of this invention are further arranged so that calls incoming over trunks in group 30 may be extended to a desired subscriber in groups 1, 2 or 3. In this case when a trunk in group 30 is taken for use the associated hunting switch in group 21 hunts for an idle link circuit of any of the links in groups 10, 11 or 12 and when connected thereto the incoming impulse will actuate the associated connector in groups 12, 13 or 15 in the same manner as when a calling subscriber in any of the groups 1, 2 and 3 desires a connection i. e. the associated connector will act as a marker if the wanted subscriber is located in group 2 or 3, or merely as a connector if the wanted subscriber is located in group 1.

Similarly connections may be extended from subscriber in groups 1, 2 or 3 to distant central ofiices over trunks in group 32. In this case the trunk hunting switch 22 extends rotary magnet 218, upper winding of relay armature and back contact. The closing of the off-normal contacts connects ground to lead 213. Relay 217 in releasing causes the release of vertical magnet 219 and this in turn causes the operation of relay 217. Relay 217 and vertical magnet 219 now operate and release alternately until brush 216 reaches the contact in the commutator 205representing the level in which the calling subscribers line is located. At this time brush 216 encounters ground from the upper armature and front contact of relay 204. Relay 217 is thereby held operated over a circuit from battery through the upper winding of relay 217, upper inner armature and back contact of 212, upper inner armature and front contact of relay 210, brush 216, the proper contact in commutator 205, upper inner armature and front contact of relay 204, to ground. Relay 212 operates in series with relay 217 over the above circuit and provides a locking circuit for itself in series with the winding of the vertical magnet 219 as follows: battery, winding of vertical magnet 219, lower wim ing of relay 212, lower inner armature and front contact of this relay, to ground at relay 210. The original circuit for the vertical magnet is now open, so under these circumstances it will release as it does not receive sufficientcurrent with relay 212 in its circuit. Relay 212 in operating places the rotary magnet 218 under control of relay 217 and this relay and rotary magnet will now operate and release alternately until brushes 208 or 209 find battery on a sleeve terminal. The circuit for the rotary magnet may be traced from battery through the winding of this magnet, lower middle armature and front contact of relay 212, armature and front contact of relay 217, to ground at relay 210. When the rotary magnet operates relay 217' is released, but when battery is encountered on the sleeve of the calling subscribers line thisrelay is held operated thus preventing further operation of the rotary magnet. The holding circuit for relay 217 extends from battery through the winding of the cutoff relay 203, upper armature and front con tact of relay 202, sleeve terminal of the calling subscribers line in line finder 201, and, if it is assumed that the calling subscribers line terminals are located in thefirst hundred line group, through the sleeve brush of the set 208, upper winding of relay 221, second lower armature and back contact of relay 222, lower Winding of relay 217 to ground at rela 210. If thecalling subscribers line terminals had been located in the second group of lines the battery connection would have been supplied through the sleeve brush of the set 309, the upper winding of relay 222,

second lower-armature and back cont-act of relay 221, upper armature and back contact of relay 211, and lower winding of relay 217, to ground at relay 210.

If two subscribers whose lines terminate in the same position in the same level but in the two different groups of 100 lines are calling simultaneously both relay 221 and 222 might operate, but relay 221 will open a holding circuit for relay 222 so that relay 221. only will be operated, thus giving preference to the calling subscribers line located in the first group to which brushes 208 has access. Relays 203 and 221 operate in the holding circuit for relay 217. Relay 203 locks through its own upper inner armature and front contact, causes the release of relay 202, extends the talking conductors from the calling subscribers line to link 207, and makes the jack 228 busy. Relay 221 is energized sufficiently bythe current through its upper windin to close its inner lower armature and front contact. thereby causing its own complete operation in a circuit from battery through its lower winding, its lower inner armature and front contact, upper outer armature and front contact of rotary magnet 218 through lead 224, inner right hand armature an d make-before-break contacts of relay 306 to ground over relay 213 at relay 210. Relay 221 in operating connects the wipers 208 of the switch 201 to the link 207 at its upper armatures and front contacts.

Relay 221 also closes a circuit for the operation of relay 211 as follows: battery, upper winding of relay 211, lower outer armature and front contact of relay 221, to ground at the off-normal contacts 226. Relay 211 provides a locking circuit for itself from battery through its lower winding, lower inner armature and front contact, over the start lead, to ground at relay 206. This circuit is not used unless relay 204 is operated by another subscribers line relay and this line finder is released during the period that the ground on the start lead is needed for the seizing of another line finder as will hereinafter be described. It should be noted that ordinarily relay 204 will by this time he released due to the release of line relay 202. Relay 211 in operating opens the start lead connection for relay 210 and connects ground from lead 224, through the upper armature and front contact of relay 211, lower middle armature and front contact of relay 221. to the sleeve brush 208. This is a busy ground for the calling subscribers line. The release of relay 210 causes the release of relay 217 and rotary magnet 218, the circuit for relay 217 being opened at the outer lower armature of relay 210 and the circuit for the rotary magnet being opened at the armature and front contact of relay 217. Another locking circuit is now closed for relay 221, independent of the connection hereinbefore traced through the upper outer armature and front contact of the rotary magnet 218. This circuit may be traced from brushes are stepped up to the first level, the

off-normal contacts 41.3 are operated and the original circuit for vertical magnet 412 and relay 411 now extends through the right hand armature and front contact of relay 411 and closed contacts of the off-normal contacts 413, to ground at relay 405. hen relay 405 operates after the first impulse the Vertical magnet 412 is released, but relay 411 is slow to release and remains operated during the second impulse. Relay 407 is locked in operated position through its inner right hand armature and front contact. to ground through closed contacts of off-normal contacts 413. The second impulse again operates the vertical magnet 412 and advances the brush 415 to the second terminal of commutator 416. At the end of this impulse relay 411 releases with the vertical magnet. Relay 406 is now operated over a circuit from battery, winding of this relay, second contact of commutator 416, brush 415, outer right hand armature and front contact of relay 407, make-beforc-break contacts of the release magnet 418, second lower armature and back contact of relay 419, right hand armature and back contact of relay 411, to ground. Relay 406 in operating closes a cir- 'cuit for release magnet 418 from battery through the winding of this magnet, closed contacts of off-normal contacts 413, second left hand armature and front contact of relay 406, inner left hand armature and front contact of relay 407, to ground. Relay 406 also opens the dial tone circuit and provides a locking circuit for itself, through its right hand'armature and front contact to ground at the outer left hand armature and front contact to relay 410, so this relay will remain operated during the succeeding operations of the switch. hen the switch returns to normal, due to the operation of the release magnet, relay 40'. is released by the restorin of the off-normal contacts 413 to normal and it will be'noted that relay 407 Wlll not be operated during the succeeding operations of the switch as the original connection therefor through the outer left hand armatureand back contact of relay 406 is broken.

The switch having" been returned to normal will now be a 'ain operated by the second number dialed, Wliichmay be any one of the digits/1 to 0. In this case the circuits for thevertioal magnetand relay 411 will be controlled by the second digit in the number called in the same manner as hereinbefcre described, and advance the brushes of switch 401 to the desired level.

lVhenthe brushes of the switch 401 have reached this level and relay 411 is released,

the release of relay 405, in response to the first impulse of the last di 'it of the code number completes a circuit for oncratnw the rotary. magnet 420 from battery through the winding of this magnet, lower outer armature and back contact of relay 410. lower outer arn'iature and back contact of relay 422, outer left hand armature and bacl; contact of relay 407, left hand arnia'tin'e and back contact of relay 411, closed contacts of off-normal contacts 413, right hand armature and front contact of relay 410, arn'iai'ure and front contact of relay 405, to ground. This will advance the two sets of brushes 424- and 425 of the connector 401 to en ige the corresponding terminals of the first line in the selected level, but, as relay 423 is not operated at this time, only the set of brushes 421 will be actively engaged. The succeeding inipulses received from the calling subscriber will operate the rotary magnet 420 to select the terminals of the desired line in this level. for example line 400.

Relay 426 is also operated at the first operation of rotary magnet 420 from battery through the winding of this relay to the ground at relay 405 as hereinbefore traced for the rotary magnet. Relay 426 slow to release so that it will remain operated during succeeding operations of the rotary net 420. The operation of this relay (isconnects the sleeve brush of the set of brushes 424 from the upper winding of relay 422 and connects it through to the winding of relay 419. The closing of the lower armature and front contact of relay 426 makes the operat ing circuit of this relay independent of the lower armature and back contact of relay 419 so as to prevent the release of relay 420 if the test brush engages the terminal of a busy line during the advance of the brushes to the terminals of the called line.

hen this last series of impulses is con1- pleted relay 426 releases and if the called line is busy at this time relay 410 will operate from ground on the sleeve terminal of this busy line and will remain locked under control of relay 410. The locking circuit for relay 410 may be traced from battery through the n n ing of this relay, make-beforc-hreait colilncls of relay 426, upper arn'iatnre and front contact of relay 419 to ground at relay 410. Vith relay 419 operated and relay 426 released the circuit for the test brush of the group 424 is opened and the switch is disable-.1 For further movement. A busy tone from the source 427 will be applied to the ring conductor of trunk 207 to notify the calling subscriber that the line is busy. ll hen the calling subscriber hangs up his receiver relay 405 is released, releasing relay 410. l-lelay 306 is thus released and the busy and holding ground is disconnected from lead so that relays 203 and 221 release. The line finder and connector are both restored to normal. The circuit for the. release magnet 418 of the connector is closed from battery through the winding of the olfnormal contacts 413, lower outer armature and lllltlx' ts winding, oil-normal contacts 226, heel: 221, to ground contacts of relays 210, 222 and et the oil-normal contacts 226.

ll, h-invever, the callerline is tree r slay 1119 is not operated and relay 126 released, this relay in releasing establishes e connection for the test brush (it cup 42% to ground through the upper winding of relay 4:22, upper ornn tur and heel; contact 01? relay 1:19 and outer left hand miniature andv -"rent contact of reley 110. lleluy 492 operates in series with the cute". ,-uy of the called subscribei"s line and loses toe circuit of i s holding Windin whic eiitends from bettery throw 1 its looer iil'i" g, lower inner armature one. ont contact, outer left hand ornieiiure and trout contact of reley 4:10, to ground. Holey 122 in operoting also establ shes 2r direct connection to groiu'ul for the t it brush oi the group 424: tl (high the upper arr I nature and onclc contact of relay 126, upper inner armature and front contact of reloy 122, to ground at the outer letlt hen d erinnture and front Contact 01 l-eloy no. lleley also GHlQDL the tip sud rin ln'ushes of the group 12 to the ringing circuit through the upper urinotures end buck contacts o'l' ringing relay 131, and opens the circuit for the rotary magnet 4:20 and the relay to disable the switch for further inoveinent. Ringing current is new applied from the source through the upper Winding of the ri" i'ng relay 431 over the tip conductor to the culled subscribefis line and heel; over the ring conductor to ground.

l l hen the oiled subscriber answers the increase in current in upper winding of relay (till is sullicient to operate this relay to close at locking circuit from better y tliirough the lower Wind g, lower ern'ietui end trout contact, to r d the outer left hand orinuture end lit contact of relay 4:10. This locl 1g circuit '01 etes the operation of r :Jlf' the connection for the uhscrihcr to eel. lip end ri g coi'iduci to trod: 2E7. This connect the two lir es "og'ether conversw rng current ooing supplied to the c llec subscriber through relay n.3, the circu t hcing lrcni l; through the lower Winding of ll! 5 r-,-..e to the ring conductor oil heel; over the tie conductor through the Winding, lower zirnioture and front i T :t of relay 131, to grou an at relay 11.0. lleloy i 1. ground con-- crates and supplies nectiou for its *ircuit indepei lent ct rcloy ll ind t-he relezuie circuit.

l hen the ceiling subscriber hon gs up, relay 10:; is released, causing the release of relay 110. 'lhis relay causes the release oi the liie finder (Fig. 2) by removing ground from lends which causes the releose of: relay 221. and the operation of release magnet 218 over a. circuit from battery through the W1 ing of this magnet, otl-norznel contacts 22c, upper outer ernurture and beck contact of the start relay 210,1owe aruintures and heel: contacts 01? relays 222 and 2-21 in series, to ground at the oil-normal contacts 226. l i hen the release magnet has operated and the line finder is returned to normal this circuit opened at the oil-normal contacts 226. The 7 groiuid being removed from conductor 22% causes the cut-oil relay 203 of the calling subscribers line to release end else the release of relay 806. In case the sort lead is grounded at this time, relay 211 is held oper-- Q sited until this groiuid reiiuoved, in order to prevent interference with the line finder under control thereof. ll the called subscriber hes not yet hung up, ground is inninteined on lead 213 by the connection through the lneke-betore-brcok contacts of relay 306, and the inner loWe. armature n id front contact 0'1 reluy 128 to hold rel uy 211 operated and thus prey nt the line tinder 201 from being operated until trunk 2107 is iinelly released at the connector end.

When the called subscriber hangs up, role 128 released, causing the release of relay 211 if not held up by ground on the start lead and also the release of all the other reloys, such as relays 131, 106 and 122. A circuit is also closed for the release magnet 118 as lollows: battery through the Winding of this magnet, ol'l-norinul contacts 413, outer lower erniotur and back contact of relay 4:28., right hand orinntures and l eel: contacts of rcluys 110 and 4:05, to ground. When the connector is restored to norn'uil the oil-norniel contacts 413 release opening the circuit tor the release magnet.

Referring now to the extension of connections in which the connector is us d as e mail:- ing switch, the extension of e connection to the P. X. operotors position 500 will be explained. This connection corresponds to a connection to position 29., 1, h creinhefore described. lhe circuits shown. in l-Fig. 3 and Fig. 5 are used tor extension oil. connections of this type. In this particular case the calling subscriber will diel o code uuiuliier 115 which, according to the urreng e 3e :5 ot the connector, is number 9. ln dish; this nine-- her the connector will be (secreted to sdmnce the brush 415, over the conunututor l1 G to the 9th terminal. ll lieu this terminal is reached back contact of relay 111 to ground. Relay 312 now operates to remove the ground from the test lead 314 and the corresponding terminal of hunting switch 502 and to close 7 hand armature and front contact of relay 312, to ground at the lower armature and back contact of relay 310. The hunting switch 502 and others in the same and other groups are of the single motion rotary switch type havlng no normal position. Switch 502 is connected to link 501 terminating in jack 516 at v the operators position 500. Relay 504, in

operating, closes a circuit for the stepping magnet 506 through the winding of this magnet and its self-interrupting contacts, outer left hand armature and front contact of relay 504, lower outer armature and back contact of relay 507, to the test brush of switch 502. Another circuit for magnet 506 is completed through the winding of relay 507 to ground at the inner left hand armature and front contact of relay 504:. If the brushes of switch 502 are at the time resting on the terminals of another connection to a circuit such as shown in Fig. 3 ground will be en countered'on the test lead corresponding to lead 314 at the right hand armature and back contact of the relay corresponding to relay 312 so that the stepping magnet 506 will be operatedto advance the brushes of switch 502 to the terminals of the next connection. This operation is repeated as long as the sleeve brush of switch 502 encounters ground on succeeding sets of terminals.

When the calling line is found there is no ground on test lead 314 sothat magnet 506 will not operate further and the switch stops with its brushes in contact with the calling line. The ground applied through relay 507 will now cause relay 507 to operate whereas magnet 506 will not receive sufficient current for operation. The original connection for the magnet 506 to the test brush of switch 502 is thereby opened at the lower outer armature and back contact of relay 507. Relay 507 in operating closes a connection from ground at the start relay 504, through its outer lower armature and front contact to the test brush of switch 502 so that relay 310 will now'operate, over a circuit from battery, through the winding of relay 310, right hand winding and right hand armature and front contact of relay 312, test lead 314:, test brush of switch 502, to this ground. Relay 312 holds in this circuit and relay 310 opens the connection through trunk 207 leading to the connector in Fig. 4 so that the connector will now be released by the release of relay 4.05 in the manner hereinbefore described. The releaseof the connector would ordinarily release relay 306 and cause the release of the line finder in Fig. 2 but relay 310 in operating closes a. holding circuit for relay 306 so as to prevent its release and the release of the line finder. Relay 310 also opens the start circuit at its lower armature and back contact.

The connection will now therefore be extended from the calling subscriber over a portion of trunk 207, tip and ring conductors 317, switch 502, the upper and lower inner armatures and front contacts of relay 507, make-beforc-break contacts of rela y 500, and windings of relay 510, to battery and ground. Relay 510 is therefore operated at this time thro h the calling subscribers loop and in ng provides a ground coni'iection at its lci't hand arn'iature and front contact for holding relay 507 operated, as it will be noted that when relay 310 operated to open the start circuit, relay 50% was released. Relay 505 was operated over an obvious circuit through the operation of relay 507, so that the start lead 31% is new extended through the outer left hand armature and front contact of relay 505 to the next switch.- The start lead extension is marked 512. In this manner relays 507 and 505 are now held under control of relay 510. Relay 510 in operating closes an obvious circuit for lighting of lamp 515 to indicate to the l". B. X. operator that a connection is desired over this circuit.

lVhen the operator answers this call by inserting plug 5 5 into jack 516, relay 500 operated over an obvious circuit through jack springs closed at this time; and this opens the circuit for the lamp 513 which is extinguished and also opens the connections through the windings of relay 510 from the calling subscriber. The connection from the calling subscriber is now extended over the tip and ring terminals of jack 516 and plug 515 through the windings of relay 517 to battery and ground and this relay in operating prevents the lighting of supervisory lamp 518. The connection from th s point on is of no importance as far as this invention is concerned. It is suiiicient to say that the connection may be extended to the l7. 1%. X. operators telephone set and conversation between the calling subscriber and this operator may begin. Talking current for the calling subscriber is supplied through the windings of relay 517. It should be noted that relay 510 is not released at this time but held operated through contacts of relay 509 and this relay in turn holds the relays 507 and 505 operated. It should be mentioned here that if all? ofthe hunting switches in this group are busy the start lead extension of the last switch. in the: group corresponding to ex tension 512 is connected to lead330; Gonsequently, if a call is made 111K161;thGSG ClICLUII- stances (ground over-the lead 315; wilhbe supplied through a; circuit; closedf tln'oughthe outer left} he ndarmatures and front contacts of; all relayscorresponding to i-clay. 505,.lead 330,..outer left hand; armature and front; contactof the relay; corresponding to relay 312 in the link circuit through which the call is made-, the conductor corresponding tov condoctor-328 make-befonebrealccontactsvof the relays corresponding to relays 419- and 426 the wii'idingofthe relay, corresponding to relay-419 to battery-,,causing; this relay to 0p erate and apply busy signal to the calling line.

\Whenthe operator disconnects, relay 509 is released and if the calling subscriber hangs up-relays 5-10,- 507 and 505-are also released. Ehe groundis thereby removed" from the test brushand relays 31,0 and 312 are released.

. Relay 310 releases relay 306 which in turn causes the'release of the line finder as hereinbefore described.

Referring now to a connection from a calling subscriber to ithetie-line asshownin Fig. 6, this subscriber will operate a connector as hereinbefore describedtd advance it in a Vertical direction to position 10. This is the position in which the connector will act as a;- marking switch to establish connections to tie lines corresponding to" the group 30 in Fig. 1. Inthis case circuit will be completed for the operation of relay 320 as follows; battery, left hand winding of this relay,i lead32l-, the 10th contact of commutator 4. 16 brush L15, outer right hand armature andfront contact. of relay 407, ma ke-bcforebreak contact of release magnet llS, second lowerarmature and back contact of relay 419, righthand armature and back contact of; relay 41L, to ground'. Relay 320.111 operating opens the connection to ground forthe test lead 322 and extends it through its own right handwinding and the winding of relay 3.10110 battery; Relay 320 -alsotestablishesi a connection fonthe start lead 323 from ground at the lower armature and back; contact of relay 310: This; start lead is connected. to the-start relay 603 oft'he first choicehunting switch 602.. Relay 603 operates and closes obvious circuit for-the operation of relay 608. Thisrelay in operating-extends a conncctienfon the tie-line 600-, as is obvious over armatures and backcon-t-actsof FGlZLYStGlZiELDCl 605;.throughathezwindingsiofrrelays 610 to battery and; ground. This. latter relay operates in serieswitlr a relay,notshown, but; usually bridgech acrossthedistant en-dof the tie-line. An obvious circuit is: closed by the operation of: Inlay-610 for the: relay- 6E1 which in open closes a leaking; circuit. for relay 608,

Relay 611 closes a circuit from ground, through its lower armature and front contact, the outer left hand armature and front contact of relay 603, winding of relay 605, self-interrupting contacts and winding of stepping magnet 604e, to battery. Another circuit closed through the operation of relay 603 for the stepping magnet 604: may be traced from battery, winding and self-inter rupting contacts of this magnet, inner left hand armature and front contact of relay 603, lower outer armature and back contact of relay 605, lower inner armature and back contact of relay 606 to the test brush 624 of switch 602.

If the switch 602 is connected to the terminals of any other line rather than tothe one associated with the circuit in Fig. 3, ground will be found on the corresponding test terminal thereof and thus complete a cir cuitj for the stepping magnet a to advance it from one set of terminals to another until it reaches the line from the circuit of Fig. 3 the ground having been removed from the test terminal by. the above mentioned opera tion of relay 320. Under these circumstances relay 605 does not operate as it is short cirouited by the ground on the corresponding test terminals. When terminal 62 i is reached'a circuit is established for the holding of. relay 320 and the operation of relays 310-and 605 overa circuit as follows: from battery, through the winding of relay 310, right hand winding of relay 320 and right hand armature and front contact thereof, test lead 322 test terminal andbrush 624- of switch 602; lower inner armature and back contact of relay, 606, lower outer armature and back contact of relay 605, inner left hand armature and front contact of relay 603, winding of relay 605, outer left hand armature and front contact of relay 608, to ground at the lower armature and front contact of relay 611. Relay 605 asstated will now operate but magnet 604: will not operate as its winding is now in series with that of relay 605 to ground at relay 611 and in parallel with that of relay 310 to battery. It will be noted that when relay 605 operates the ground at relay611 is extended through the lower outer armature and front contact to test brush 62. and through the next to the lower armature and front contact of relay 605 tolock this relay operated under control: of relay 611. Relay 310 and relay 605 are thereby held operated 1 from thisground at relay 611 independent of the contactsof relay 603; Inthese circumstances; asstated, magnet 605 will not operate and switch. 602 will come to rest on the terminals of the line associated with the circuit of Fig. 3.

Relay 605 in. operating closes obvious. circuits for the operation of relays: 612 and 613;. Relays 605 and 613 connect the calling line through the tipi and: ring terminals of switch 602 and through the windings of relay 610 to battery and ground, and relay 613 removes the short circuits for the condensers 615 and 616. Relay 610 will now be held operated from the calling subscribers line while the holding coil 617 is bridged across the tie-line 600 through the upper armature and front contact of relay 610, and upper inner armature-and front contact of relay 613. Relay 612 opens the circuit for and thereby releases the start relay 603 and 7 release.

extends the start lead through lead 619 to the next switch. Relay 611 and, through it, relays 605, 310, 320, 612, 613 and 608 are now under control of relay 610.

At the operation of relay 310 the connector in Fig. 4 releases as hereinbefore described and when the subscriber dials to extend a connection over tie-line 600 to the distant exchange the impulses incoming from the calling subscriber operate relay 610 and these impulses are repeated over the tie-line by the alternate opening and closing of the connection through the bridgeholding coil 617. Relay 618 is operated on the first release of relay 610 so as to short circuitthe bridge coil 617 during pulsing. Relays 618 and 611 and consequently relays 605, 612, 613 and 608 remain operated during pulsing and all of these relays except relay 618 remain operated during conversation. Relays 618 and 611 are for these purposes made slow-tolVhen the calling subscriber hangs up his 1 receiver relay 610 isreleased operating relay so that the relays 320 and'310 release and cause therelease of relay 306 which in turn causes the release of line finder 302 as hereinbefore described.

If the tiesline 600 is used for incoming calls to the P. B. X., battery and ground connections are applied from the distant end of this trunk causing the operation of relay 621. Relay 621 in operating closes obvious circuits for the operation of relays 606 and 611. Relay 606 closes a locking circuit for itself under control of. relay 611 and causes the operation of relay 612 from battery, through the upper'winding of this relay, through the upper outer armature and front contact of relay 606 'to ground at the lower armature and front contact of relay 611. Relay 612 in operating advances the start lead 323 to the next switch over lead 619.

Apparatus at the distant end of the trunk 600 now functions to remove battery and ground from the line and place a holding bridge across it. Relay 621 is thereby released, causing the operation of relay 603.

This relay in turn causes the operation of relay 608. The circuit for relay 603 may be traced as follows: battery, winding of relay 603, outer lower armature and front contact of relay 606, and lower outer armature and back contact of relay 621 to ground. The circuit for the operation of relay 608 is from battery through its upper winding to ground through the right hand armature and front contact of relay 603. Relay 60S locks under control of relay 611.

In operating relay 608 connects the trunk to relay 610 which now operates over a circuit as hereinbefore described. Relay 610 in operating prevents the release of relay 611. Relay 611 is slow-to-release so that it is held up during'the interval between the release of relay 621 and the operation of relay 610. and this relay thus keeps the relays 606. 608 and 612 operated. Relay 603 closes a circuit for the stepping magnet 604 and relay 605 to ground at relay 611. f the link circuit, with which switch 602 is connected, is busy this circuit is also closed through the inner left hand armature and front contact of relay 603, the lower inner armature and front contact of relay 606, test brush 623 of switch 602, lead 324, to ground on lead 224 through the con- 1 acts of relay 306. If other leads corresponding to lead 324 of other circuits of this kind supply ground said circuits are also busy and not until an idle circuit is encountered will the ground be removed. The switch 602 will therefore hunt for the first idle circuit in the manner described for an original call except that in this case a test is made over brush 623 instead of brush 624 as relay 606 is operated. When the idle circuit is found relay 605 operates and connects the trunk 600 directly to a connector switch and disconnects relay 610 at the trunk.

It will be noted that on the connection of the trunk 600 to the connector relay 405 operates over the talking leads from trunk 600 and this in turn operates relay 410 which supplies ground over lead 324 making this particular circuit busy to other incoming connections over switches like 602. This ground also keeps relays 605, 608, 606 and 612 operated. Relay 606 holds relay 603 operated so that all these relays are now not dependent on the holding ground of relay 611 which is released on the release of relay 610.

The operation of relay 306 causes the operation of relay 211 over lead 213 so as to make the line finder busy and to advance the line finder start wire to the next line finder. The calling subscriber of trunk 600 may now operate the connector to either act as a marker switch to select a wanted subscriber in the seclilJ end or third group or to sclect'a wanted subscriber in group 1 in the manner hereinbetore described. When the calling subscriber hangs up his receiver relays 405 and 41.0 release and ground is removed from lead 32% causing the release of the relays 603, 605, 606 and 008 in the circuit of trunk restoring it to normal. In. case the start lead 323 is grounded at the time the circuit is released, relay (S12 is maintained operated to prevent interference with the operations of other switches.

The next type of. connection.that.may he extendedfrom this P. ll. X. the one leading toa central otlice. A connection of this type may be reachedby dialing number 6 on the part of a calling subscriber. Connections are now established as hereinbetore described over commutator 4-16 and in this case relay 325 is operated over lea-d This relay in operating prepares connections over leads 304: to a switch similar to switch 502 which. starts hunting for the link which is thus marked by the removal of ground "from the testflead. The circuits for this switch are identical with the circuits for switch 502 and trunk 5501 up to the line marked%61bl From this point on it. is arranged accordingto Fi 6 and the operations for extending a connection over a trunk suchas 700 are identical with the opera tion for the circuit of relay 501 up to this point. Relay 701 is operated in the same manner, as relay. 510. When this relay operates a connection isextended from groun d at the inner left hand armature and front contact of relay 701. through the outer upper armature and: back contact oi relay 702, to the tip conductor ot trunh 700. 'Ihis ground connection establishes a signal at the distant central office and inany well known manner. Then the operator at this central office answers the call by establishing a battery and ground connection for theoperation of relay 703., which isbridged across the tip and ring conductor oi": trunk T00. Relay 703 in opcrau int! closesan obviouscircuit for the operation of relay 702. Relay 702 extends the tip and ring connections from the operator at the distan; end to the calling subscriber in thiseX- change. The supervisory relay 705 is thereby operated to maintain relay 701 operated. Itelay 701 is slow in releasing so that it will he maintained o 'i-erated after the release of relay 703' and operation of relay 702, until the operation. of relay 705. Relay. T01 maintains relay 702 operated over a holding circuit for this latter relay through the upper outer armature and front contact thereof. I Vilhcnthe connection is released relay 705 is released causing the release of all the relaysi'n this circuit.

It should be noted that the circuit arraluremerits shown for extendiuga connection to a centralofiice are such that in case the calling 'sul'ascriber is not permitted to call at a central office a busy tone will be transmitted to such a subscriber if he; attempts to'call. The line of the subscriber at A is arranged for such restricted service. As hereinbetore described relay 307 operates'when the subscriber at A calls. hen this subscriber attempts to make the above describedconnection to a central ofiice by dialing the number 6, relay 325 will not be operated but the connection over lead 327. will in this casebe extended tocause the operation of relay 4:19. A circuit will be extended from battery, through the winding of this relay, make-beforebrealr contact of relay 426, make betore break contact of relay 419; lead 328, upper armature and front contact of relay 307, to ground at the sixth terminal of the commutator 506, over brush 415 and. as hereinbefore described to the ground at relay 411.. Relay 119 in operating connectsa busy tone from the source 427 to be appliedt'o the ring conductor of the trunk thusnot-ifying the calling subscriber ofthis particular service condition:

What isclaimed is:

1. In a telephone system, subscribers lines, trunks, automatic switches associated with said subscribers lines, hunting switches asso ciated with saidtrunks, and means for actu ating an automatic switch in one manner to cause it to release and thereafter reactuate to connect a calling subscribers line with a called subscribers line and for actuating it in another manner to cause the hunting switch ot'an idle trunk to connect said, trunk with the calling subscribers line.

2. In a telephone system, calling lines. called lines, trunks, automatic switches associated with said subscribers lines, hunting switches associated. with said trunks, means for actuatingan automatic switch in one mannor to cause it to release and thereafter reactuato to extend the associated calling line to a called line, and means for actuating said automatic switch in. another manner to cause the hunting switch of an idletrunk to connect said trunk with said. calling line and to cause said automatic switch to be disassociated from the calling line and released.

3. In a telephone system, calling lines, called lines trunks, automatic switches associated with said lines. hunting switches associated with said. trunks, means responsive to certain series of in'ipulses received over a calling line for actuating the associated automatic switch in one manner to cause it to release and thereafter reactuate' to connect said calling line with a desired called line. and means re sponsive to certain other series of impulses received over said calling line for actuating said automaticswitch inanother mannerto cause the hunting switch of an idle trunk to connect said trunk with the callingline and to cause said automatic switch to be disasseciated from said calling line and released.

4. In a telephone system, hunting switches;

a trunk for each switch, lines terminating in each switch, means for seizing a line, means for actuating the switch of any idle trunk to connect it to said seized line, and means for actuating any switch to connect its associated trunk with an idle line. I

5. In a telephone system, hunting switches,

' a trunkfor each switch, lines terminating in tification of a line for actuating the switch of an idle trunk to connect it to said line, means for seizing a trunk, and means responsive to the seizureof said trunk for connecting it with an idle line through the associated switch. i

7. In a telephone system, subscribers" lines, trunks, automatic switches associated with said subscribers lines, hunting switches associated with said trunks, means responsive to certain impulses from a subscribers line for connecting said subscribers line through the associated automatic switch to a desired subscribers line, and responsive to certain other impulses for connecting said subscribers line to an idle trunk through the associated hunting switch, means for seizing a trunk, means responsive to the seizure of a trunk for connecting it through the associated liuntlng switch to an idle automatic switch, and means thereafter responsive to impulses from said seized trunk for extending said last mentioned connection to a desired subscribers line through said associated automatic switch.= I

8. In a telephone system, subscribers lines, line finders having access to said subscribers lines, automatic switches having access to said subscribers lines, link circuits, each connecting a line'finder with an automatic sw tch, hunting switches having access to said l nks, trunks, each terminating in a hunting switch, means for completing a connection from one subscribers lineto another through a line finder and its associated link and automatic switch, means for completing a connection from asubscribers line to an idle trunk through a line finder, the associated link and the hunting switch associated with said idle trunk, and means for completing a connection from a trunk to a subscribers line through the associated hunting switch, a link and its associated automatic switch.

9. In a telephone-system, subscribers lines, trunks divided into groups, automatic switches associated with said subscribers lines, hunting switches associated with said trunks, means for. actuating an automatic switch in one manner to connect a calling subscribers line with a called subscribers line, and in another manner to mark a group of trunks and cause the hunting switch of an idle trunk in the marked group to connect said trunk to the calling subscribers line.

10. In a telephone system, si'ibscribers lines, trunks, subscribers line finders, a link circuit associated with each line finder, a connector associated with each link, a hunting switch associated with each trunk and having access to said links, means for extending a connection from a calling subscriber to a called subscriber including a line finder and its associated link and connector, means for extending a connection from a calling subscriber to an idle trunk including a line finder and its associated link and a hunting switch, and means whereby the associated connector is employed as a marking switch during the establishing of the last mentioned connection to start the hunting switch of an idle trunk to connect it to the link circuit and without reserving for marking any of the connecting terminals of the connector.

11. In a telephone system, groups of lines, a group of automatic switches associated with said lines and having access to a certain group of lines, other groups of automatic switches, each group having access to a certain group of other lines, a hunting switch associated with each automatic switch in said other groups of automatic switches, said hunting switches having access to all of the lines in all of said groups, means for actuating any one of said first mentioned automatic switches to connect the associated line with any line to which said automatic switch has access, and means for actuating any one of said first mentioned automatic switches in a different manner to cause an idle hunting switch to connect the automatic switch associated therewith to the line associated with the actuated first mentioned automatic switch.

12. In a telephone system, groups of lines, a group of automatic switches associated with said lines and having access to a certain group of lines, other groups of automatic switches, each group having access to a certain group of other lines, a hunting switch associated with each automatic switch in said other groups of automatic switches, said hunting switches having access to all of the lines in all of said groups, means for actuating any one of said first mentioned automatic switches to connect the associated line with any line to which said automatic switch has access, and means for actuating any one of said first mentioned automatic switches in a different manner to cause an idle hunting switch to connect the automatic switch associated therewith to the line associated with the actuated first mentioned automatic switch, and means for actuating the automatic switch associated EDWARD E. HINRICHSEN. 

